About KOH..

Ontheway · Dec 11, 2015

Hi all,

According to this, KOH is able to adsorb CO2 and water from air.

Do you know any use of KOH to reduce CO2 in the effluent of reactors, or increase pH in tank water by adsorbing excess CO2?

Randy Holmes-Farley · Dec 11, 2015

KOH is potassium hydroxide. Only the hydroxide part is important in this context, so other hydroxides will act similarly. Sodium hydroxide (lye) and calcium hydroxide (used to make limewater/kalkwasser) behave similarly, at least when added to tank water.

When added to an aquarium, it will boost alkalinity, and it will boost pH. It boosts pH by combining with CO2 and bicarbonate to form bicarboante and carbonate. So at least temporarily it raises pH (just as limewater/kalkwasser does). But the limitation is that it also adds alkalinity, so you cannot add too much. Adding 0.5 meq/L of hydroxide adds 0.5 meq/L (1.4 dKH) of alkalinity and will instantly boost pH by about 0.6 pH units.

Aquavitro Balance is a product like this, but they neglect to tell users that it boosts alkalinity, which is a problem, IMO.

http://www.aquavitro.com/products/balance.html

I personally would not generally recommend using these products, but would use limewater/kalkwasser, since they add alkalinity and not calcium. They are also very easy to overdose, while limewater is not since it is necessarily more dilute.

Randy Holmes-Farley · Dec 11, 2015

Oh, and in case I wasn't clear, KOH and NaOH will dissolve into tank water with almost no limit, so one cannot add the solids to the tank water or reactor effluent as one would use a binder like GFO.